It later emerged he was on bail for firearms offences and was suffering from post-traumatic stress disorder (PTSD).

A BBC investigation claimed G4S was aware of failings in its screening procedures months before the shooting.

Fitzsimons is currently serving a 20-year sentence in Iraq for the murders.

Danny’s step-mother Liz Fitzsimons , of Whitworth, said: “I would really like to see a public inquiry into this. There were 10 criteria they were supposed to have ticked, but there were only three completed. I am angry and upset because if they had done that properly, we wouldn’t be in the situation we are – and Paul McGuigan’s mum wouldn’t have lost her son.”

The investigation claims G4S never received a criminal records bureau certificate which would have highlighted the fact he was on bail for the firearms offences.

It also claims the company did two audits in March 2009, the first of which found screening procedures only obtained “basic disclosure of criminal records” and “a number of personal files did not include criminal records checks.”

Liz said: “He did have bizarre behaviours but we didn’t understand the severity of them at the time because we weren’t better educated about PTSD. I think the Army has let him down, we’ve let him down and in fact, he’s been let down all the way.”

She added: “I would like to see some positives coming out of this situation after G4S has made such a mess of things.

“I would hate something like this to happen to someone else – we are a normal, honest, hard-working family and we are not hooligans.”